[ntp:questions] Sure gps looses all sattelite fixes

unruh unruh at invalid.ca
Fri Feb 24 20:17:26 UTC 2012

On 2012-02-24, David J Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
> "unruh" <unruh at invalid.ca> wrote in message 
> news:cmQ1r.3572$py5.2962 at newsfe09.iad...
> []
>> The graphs of the signal strengths at the edges of these dropouts is in
>> ftp://theory.physics.ubc.ca/outgoing/drop{out,in}.pdf
> Could not access this page in Firefox.

These pages. 
dropout.pdf and dropin.pdf sorry if my use of the  bash syntax confused

> []
>> Is this a flaw in the Sure unit (NOte that the sure unit drops its PPS
>> signal as soon as it does not a fix. Some units-- Garmin?-- keep sending
>> out PPS based on the freerunning onboard clock for quite a while, as I 
>> understand it.
>> Teh Sure does not, which may be an advantage or a disadvantage.
>> (ntpd/chrony grab one of the other servers which produces
>> discontinuities in time when the pps comes back)
>> Is it evidence of some outside noise source (jamming?) , microwave tower
>> emission?
> That's certainly a possibility.  I would try to locate the antenna so that 
> it has a clear view of at least half the sky, preferably towards the 
> south.  You may also notice seasonal effects with foliage blocking the 
> signal more in spring and summer.

It has. I plotted the location of the satellites in the sky using S/N
bands. I can see the whole sky (ie sattelites are tracked across the
whole sky-- except for a hole in the northern sky where I guess the
satellites never go as viewed from Vancouver.) There are some trees to
the east, and they seem to reduce the S/N by about 10dB but they are
still visible and tracked even through the trees. (Cedars)

> Mine have a moderate view of the sky, being located indoors, but on the 
> top floor of a domestic residence.  Both pucks are stuck (magnetically) on 
> top of a PC, which does form a ground plane, but may also be a source of 
> electrical noise!  I haven't monitored as you have, but I suspect I see 
> the effects of a drop-out perhaps once a fortnight.

Mine are stuck to the iron flashing around the top of the building--
about 1/2 a meter wide. But that flashing is not attached to any
microwave noisy source AFAIK.

> Cheers,
> David 

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